The disclosure of Japanese Patent Application No. 2001-367231 filed on Nov. 30, 2001, and No. 2002-341644 filed on Nov. 26, 2002, each including the specification, drawings and abstract is incorporated herein by reference in its entirety.
1. Field of the Invention
The present invention relates generally to a contact lens and a method of designing the same, and is concerned with techniques for providing a contact lens that is satisfactory in shape stability and that is thin and comfortable to wear. More particularly, the present invention is concerned with a novelly shaped contact lens suitably applicable to soft contact lenses, and capable of establishing an easiness of handling and an easiness of differentiating between a front surface and a back surface thereof with the help of its shape stability, while ensuring its suitable wearing comfort as felt by a lens wearer. The present invention is also concerned with a novel method of designing the contact lens.
2. Description of the Related Art
Generally, contact lenses require to be excellent in (a) lens wearing comfort as felt by a lens wearer, and to be easy of (b) handling by fingers of the lens wearer. In order to improve the former requirement, i.e., the lens wearing comfort, it is desirable to sufficiently reduce a thickness of a contact lens (hereinafter referred to as a xe2x80x9clens thicknessxe2x80x9d where appropriate) while assuring a minimum lens thickness determined by a selected lens material, with production efficiency and durability of the contact lens taken into consideration. Such a thin contact lens is also excellent in oxygen permeability. The thin contact lens, however, may be deteriorated in its shape stability. In the case of a thin soft contact lens, particularly, it is likely that the soft contact lens, when being placed on a finger of the lens wearer to be worn on or removed from a cornea, clings to a surface of the finger of the lens wearer. This makes it difficult to handle the contact lens by the fingers and to differentiate between a front surface and a back surface of the contact lens, resulting in cumbersome operations in wearing and removal of the contact lens.
To cope with these problems, a number of solutions have been suggested. For instance, a lens thickness of a contact lens is increased by an amount enough to ensure a good handling thereof based on its good shape stability. Alternatively, an identification mark is provided on a surface of the contact lens for allowing the wearer to differentiate between the front surface and the back surface of the contact lens. The latter one enables the contact lens to be made thin with a great regard for the lens wearing comfort, while coping with the problem of insufficiency in the shape stability of the contact lens. However, these solutions are still in a level of compromises in which any one of the wearing comfort and the shape stability (or the handling of the contact lens) is sacrificed or ignored, and are not what can be called fundamental solutions. In particular, a number of specific manufacturing process and workings are needed to form the identification mark on the surface of the contact lens, undesirably pushing a manufacturing cost.
In order to achieve both of the excellent lens wearing comfort and the good handling of the contact lens, JP-A-8-286155 discloses a contact lens design wherein a peripheral zone has a lens thickness of not less than 1.2 times a lens thickness as measured at a central portion of the lens, and a front junction of an optical zone with a peripheral zone on a front surface (or a front curve surface) of the lens is offset radially outwardly from a back junction of an optical zone with a peripheral zone on a back surface (or a base curve surface) of the lens, so as to increase the thickness of the peripheral zone. Further, JP-A-11-52304 and JP-A-2000-214417 disclose another contact lens design wherein there are determined a lens thickness as measured at its central portion and a lens thickness at and a position of a part of a peripheral portion where the thickness dimension is maximized.
These contact lens designs disclosed in the above-indicated documents are unsatisfactory in achieving both of the lens wearing comfort and good handling of the contact lens. In this respect, these conventional contact lens designs are basically concerned with the lens thickness as measured at around the front junction on the front surface of the contact lens where the optical zone and the peripheral zone join together, and determine the lens thickness at around the front junction to be made larger enough to exhibit its good shape stability, but not cause considerable deterioration of the lens wearing comfort as felt by the wearer. The increase in the lens thickness at around the front junction inevitably restricts a design of optical characteristics of the optical zone, resulting in a relatively low degree of freedom in designing lens forms and powers.
Upon designing a contact lens, generally, a radius of curvature of a back surface of the lens is determined as a base curve to approximately correspond to a shape of a surface of the cornea of the lens wearer so that the contact lens is comfortable to wear and is positioned on the cornea with high stability. Then, a front surface of the lens is designed so as to give a desirable optical power to an optical zone of the lens, and so as to permit the optical zone to have a minimum thickness of the lens determined by selected materials. Since the lens thickness as measured at around an outer peripheral portion of a front optical zone of the contact lens is dimensioned to a specific value, according to the above-described documents, the thickness of the optical zone is entirely restricted or affected by the thickness of the outer peripheral portion of the optical zone, thus limiting a degree of freedom in designing the contact lens and a power of the lens.
It is therefore an object of the invention to provide a contact lens which is novel in configuration and which is capable of highly ensuring both of lens wearing comfort and shape stability, while providing a high degree of freedom in designing the contact lens.
It is another object of the present invention to provide a novel method of designing such a contact lens.
The above and/or optical objects of this invention may be attained according to at least one of the following modes of the invention. Each of those modes of the invention is numbered like the, appended claims and depending from the other mode or modes, where appropriate, to indicate possible combinations of elements or technical features of the invention. It is to be understood that the principle of the invention is not limited to these modes of the invention and combinations of the technical features, but may otherwise be recognized based on the teachings of the present invention disclosed in the entire specification and drawings or that may be recognized by those skilled in the art in the light of the present disclosure in its entirety.
(1) A contact lens comprising: a central optical zone including a front optical zone and a back optical zone; and a peripheral zone surrounding the optical zone and including a front peripheral zone and a back peripheral zone, wherein the contact lens is provided with a dioptric power P ranging from xe2x88x9210 to 0 diopters (xe2x88x9210xe2x89xa6Pxe2x89xa60), wherein the front optical zone and the front peripheral zone join together at a front junction, and the back optical zone and the back peripheral zone join together at a back junction that is located outward of the front junction in a diametric direction of the contact lens orthogonal to a center axis of the contact lens, and wherein the contact lens has a central lens thickness TC ranging from 0.03 to 0.50 mm as measured along the center axis thereof, a front junction lens thickness TFJ of not less than 0.05 mm as measured at the front junction, and a back-junction lens thickness TBJ as measured at the back junction, the back-junction lens thickness TBJ is determined depending upon the dioptric power P so as to satisfy a following expression:
xcexa3(Aixc2x710xe2x88x92ixc2x7Pi)xe2x89xa6TBJ/TFJxe2x89xa6xcexa3(Bixc2x710xe2x88x92ixc2x7Pi)
where,
A0=+1.2382
A1=xe2x88x920.1741
A2=xe2x88x921.4711
A3=xe2x88x920.9355
B0=+1.4699
B1=xe2x88x920.2523
B2=xe2x88x921.9897
B3=xe2x88x921.2603
In order to accomplish this mode of the invention, an extensive analysis or study was made by the inventors on their new finding that a shape stability of a contact lens owing to an optical zone varies depending upon a shape of a front surface of the contact lens that is determined by a dioptric power of the lens. A result of the analysis has revealed that when the front junction and the back junction are spaced away from each other in the diametric direction orthogonal to the center axis of the lens, a suitable adjustment of a ratio TBJ/TFJ of the back junction lens thickness TBJ to the front junction lens thickness TFJ depending upon the dioptric power P of the lens makes it possible to effectively ensure a desired shape stability of the contact lens at the optical zone. In this respect, the ratio TBJ/TFJ is adjusted to meet the specific condition as represented by the expression depending upon the dioptric power of the optical zone, thus making it possible to provide the contact lens that is well comfortable to wear and is fully satisfactory in its shape stability. This mode of the present invention has been accomplished based on the above-described knowledge of the present inventors.
According to this mode of the invention, moreover, the back junction formed between the back optical zone and the back peripheral zone is located radially outward of the front junction formed between the front optical zone and the front peripheral zone with a radial spacing therebetween. This arrangement makes it possible to adjust the ratio TBJ/TFJ, which is determined depending upon the dioptric power of the lens, by only shifting a position of the back junction relative to the front junction. In other words, this arrangement makes it possible to improve the shape stability of the contact lens to a required level by suitably adjusting the back junction lens thickness, while desirably determining the front junction lens thickness TFJ in order to establish required optical characteristics in the optical zone of the lens, and while eliminating adverse effect on the optical characteristics of the optical zone.
The central lens thickness TC of the contact lens is held within a range of 0.03-0.50 mm, more preferably 0.05-0.50 mm, while the front junction lens thickness TFJ where the front optical zone and the front peripheral zone join together is not smaller than 0.05 mm more preferably not smaller than 0.10 mm. This arrangement enables the contact lens to have the approximately same form and lens thickness in its optical zone, depending upon its dioptric power, thus making it possible to systematically and accurately recognize shape stability generated in the optical zone based on the dioptric power of the contact lens. Therefore, shape stability to be generated in the peripheral zone can be determined while taking into account the shape stability of the optical zone, thus enabling the contact lens to stably establish a desired shape stability in its entirety, which is enough to ensure a good handling of the contact lens.
Therefore, the contact lens constructed according to this mode of the invention can effectively establish a preferable shape stability in its entirety that is determined with the shape stability of the optical zone taken into consideration, thus eliminating the conventionally experienced problems that an excessively large lens thickness causes an excessively increased shape stability of the lens and a resultant deterioration in lens wearing comfort, and adverse effects on optical characteristics of the lens. For this reason, the contact lens according to this mode of the invention is superiorly comfortable to wear and excellent in handling as well.
A type and a material of the contact lens according to this mode of the invention are not particularly limited, and the principle of the present mode of the invention may be applicable to various types of known contact lenses including contact lenses for treating myopia, presbyopia, and astigmatism. The term xe2x80x9clens thicknessxe2x80x9d should be interpreted to mean a thickness of a contact lens measured in a radial direction at an optional measuring point. In the case where a contact lens has a spherical back optical zone, the lens thickness of the contact lens is defined by a thickness of the lens as measured along a straight line extending through a center of the spherical back optical zone and a measuring point, for example. In the case where a contact lens has an aspherical back optical zone, the lens thickness is defined by a thickness of the lens as measured along a straight line including a center of a vertex sphere as a starting point. The reasons why the present mode of the invention is directed to contact lenses having dioptric powers within a range of xe2x88x9210-0 diopters (xe2x88x9210xe2x89xa6Pxe2x89xa60) are that a great demand exists for these contact lenses usable for treating myopia, and that these contact lenses can be supplied to the market as a design family of contact lenses whose dioptric powers vary from one another at given equal intervals.
(2) A contact lens comprising: a central optical zone including a front optical zone and a back optical zone; and a peripheral zone surrounding the optical zone and including a front peripheral zone and a back peripheral zone, wherein the contact lens is provided with a dioptric power P ranging from xe2x88x926 to 0 diopters (xe2x88x926xe2x89xa6Pxe2x89xa60), wherein the front optical zone and the front peripheral zone join together at a front junction, and the back optical zone and the back peripheral zone join together at a back junction that is located outward of the front junction in a diametric direction of the contact lens orthogonal to a center axis of the contact lens, and wherein the contact lens has a central lens thickness TC ranging from 0.03 to 0.50 mm, more preferably 0.05 to 0.50 mm, as measured along the center axis thereof, a front junction lens thickness TFJ of not less than 0.05 mm as measured at the front junction between the front optical zone and the front peripheral zone, and a back-junction lens thickness TBJ as measured at the back junction is determined so as to satisfy a following expression:
TBJ/TFJxe2x89xa71
Like the above-indicated mode (1) of the invention, the principle of this mode of the invention has been accomplished as a result of the extensive analysis or study conducted by the inventors based on the technical concept that a suitable adjustment of the ratio TBJ/TFJ of the back junction lens thickness TBJ to the front junction lens thickness TFJ depending upon the dioptric power of the lens permits the contact lens to effectively establish its overall shape stability, while eliminating the problem of deterioration of the lens wearing comfort due to the excessive enlargement of the lens thickness. More particularly, the principle of this mode of the invention has been developed based on a new finding that the contact lens provided with the dioptric power P ranging from xe2x88x926 to 0 diopters (xe2x88x926xe2x89xa6Pxe2x89xa60) may suffer from difficulty in exhibiting an effective shape stabilizing characteristics or capability in its optical zone, when being provided with a suitable form and thickness at its optical zone. The reasons why the present mode of the invention is directed to contact lenses having dioptric powers within a range of xe2x88x926-0 diopters (xe2x88x926xe2x89xa6Pxe2x89xa60) are that a great demand exists for these contact lenses usable for treating myopia, and that the present inventors have paid their attention to a new finding that the contact lenses having dioptric powers within a range of xe2x88x926-0 diopters, among the contact lenses having the dioptric powers within a range of xe2x88x9210-0 diopters (xe2x88x9210xe2x89xa6Pxe2x89xa60), especially suffer from their common difficulty in establishing a desired shape stability in their optical zones. Described in detail, in each of the contact lenses having the dioptric powers ranging from xe2x88x926 to 0 diopters, the optical zone has a relatively small difference between its minimum thickness and its maximum thickness, so that the optical zone is capable of ensuring a lens wearing comfort, but is incapable of exhibiting a desired shape stability, if the minimum thickness of the optical zone is set to a minimum value required for ensuring strength and durability of the contact lens.
In the contact lens constructed according to this mode of the invention, the back junction lens thickness TBJ as a lens thickness measured at the back junction is made larger than the front junction lens thickness TFJ as a lens thickness measured at the front junction, while the optical zone is desirably designed in terms of its shape and a thickness dimension. While the desirably shaped optical zone of the contact lens is prone to be insufficient in its shape stability, the peripheral zone of the contact lens where the lens thickness is made larger at the back junction rather than at the front junction, can effectively compensate the insufficient shape stability of the contact lens. Thus, the contact lens of this mode of the invention is able to establish a desired shape stability in its entirety and a resultant good handling thereof, while being highly satisfactory in terms of its optical characteristics and its wearing comfort with the help of a reduced thickness of the optical zone. In this respect, an upper limit of the ratio TBJ/TFJ is determined while taking into account lens wearing comforts as felt by lens wearers, and a variation in sensitivities or the like of individual wearers. In general, the front and back junction lens thicknesses TFJ. TBJ have respective minimum values restricted by required lens strength and durability varying depending upon a material of the contact lens, and respective maximum values restricted by the lens wearing comfort not to be larger than 1.0 mm. For this reason, there is no need to especially consider the upper limit of the ratio TBJ/TFJ.
(3) A contact lens according to the above-indicated mode (1) or (2), wherein the front junction has a diameter within a range of 55-85% of a diameter of the contact lens, and the back junction has a diameter within a range of 70-90% of the diameter of the contact lens. Upon setting a variety of dioptric power of the contact lens, this arrangement ensures the contact lens to establish a desired shape stability in its entirety, since one or both of the shape stabilities exhibiting in the optical zone and the peripheral zone can be compensated by the other or with each other.
(4) A contact lens comprising: a central optical zone including a front optical zone and a back optical zone; and a peripheral zone surrounding the optical zone and including a front peripheral zone and a back peripheral zone, wherein the contact lens is provided with a dioptric power P not larger than xe2x88x9210 diopters (P less than xe2x88x9210), wherein the front optical zone and the front peripheral zone join together at a front junction, and the back optical zone and the back peripheral zone join together at a back junction that is located outward of the front junction in a diametric direction of the contact lens orthogonal to a center axis of the contact lens, and wherein the contact lens has a central lens thickness TC ranging from 0.03 to 0.50 mm as measured along the center axis thereof, a front junction lens thickness TFJ of not less than 0.05 mm as measured at the front junction, and a back-junction lens thickness TBJ as measured at the back junction, the back-junction lens thickness TBJ is determined depending upon the dioptric power P so as to satisfy a following expression:
(a) where the front optical zone has a diameter DFOZ of smaller than 7.0 mm (DFOZ less than 7.0 mm),
0.877xe2x89xa6TBJ/TFJxe2x89xa60.993
(b) where the front optical zone has a diameter DFOZ of not smaller than 7.0 mm (DFOZxe2x89xa77.0 mm),
xcexa3(Aixc2x710xe2x88x92ixc2x7Pi)xe2x89xa6TBJ/TFJxe2x89xa6xcexa3(Bixc2x710xe2x88x92ixc2x7Pi)
where,
A0=+1.7980
A1=+1.4330
A2=+0.5824
A3=+0.0814
B0=+2.0184
B1=+1.5827
B2=+0.6298
B3=+0.0871
According to this mode of the invention, a so-called xe2x80x9chigh-minus lensxe2x80x9d provided with a negative refractive power larger than xe2x88x9210 diopters can exhibit an excellent shape stability in its entirety, like in the above-indicated mode (1), since a shape stability generated in the optical zone can be recognized and effectively compensated by a shape stability generated in the peripheral zone with the recognized shape stability of the optical zone utilized. In addition, the peripheral zone is shaped so as to meet specific conditions selected based on the dioptric power given to the optical zone, thus making it possible to establish the excellent shape stability of the contact lens, while assuring a sufficient degree of freedom in designing the optical characteristics of the optical zone, and an excellent lens wearing comfort.
It should be appreciated that the peripheral zone is shaped with the diameter DFOZ of the front optical zone taken into consideration, making it possible to suitably compensate the shape stability generated in the optical zone by the peripheral zone with the help of the accurate recognition of the shape stability in the optical zone, without causing an excessive increase in the thickness of the peripheral zone. Thus, the contact lens constructed according to this mode of the invention is capable of exhibiting the excellent shape stability in its entirety and the excellent lens wearing comfort, as well. More specifically described, in the case where the optical zone of the contact lens has a relatively large diameter DFOZ, the thickness of a peripheral portion of the optical zone is inevitably made large sufficiently, since the negative refractive power given to the optical zone is great. Thus, the contact lens can be designed so as to exhibit its entire shape stability by utilizing the shape stability eventually generated in the optical zone, and so as to establish the excellent lens wearing comfort without needing the excessive increase in the thickness of the peripheral zone, which is likely to be caused. In the case where the optical zone of the contact lens has a relatively small diameter DFOZ, on the other hand, the contact lens can be designed such that a tendency of lacking in the shape stability generated in the optical zone can be compensated by the peripheral zone.
(5) A contact lens comprising: a central optical zone including a front optical zone and a back optical zone; and a peripheral zone surrounding the optical zone and including a front peripheral zone and a back peripheral zone, wherein the contact lens is provided with a dioptric power P larger than 0 diopters (0 less than P), wherein the front optical zone and the front peripheral zone join together at a front junction, and the back optical zone and the back peripheral zone join together at a back junction that is located outward of the front junction in a diametric direction of the contact lens orthogonal to a center axis of the contact lens, and wherein the contact lens has a central lens thickness TC ranging from 0.03 to 0.50 mm as measured along the center axis thereof, a front junction lens thickness TFJ of not less than 0.05 mm as measured at the front junction, and a back-junction lens thickness TBJ as measured at the back junction, the back-junction lens thickness TBJ is determined depending upon the dioptric power P so as to satisfy a following expression:
(a) where the front optical zone has a diameter DFOZ of smaller than 7.0 mm (DFOZ less than 7.0 mm),
1.238xe2x89xa6TBJ/TFJxe2x89xa61.470
(b) where the front optical zone has a diameter DFOZ of not smaller than 7.0 mm (DFOZxe2x89xa77.0 mm),
xcexa3(Aixc2x710xe2x88x921xc2x7Pi)xe2x89xa6TBJ/TFJxe2x89xa6xcexa3(Bixc2x710xe2x88x92ixc2x7Pi)
where,
A0=+1.2066
A1=xe2x88x920.0398
A2=xe2x88x920.1341
A3=+0.0139
B0=+1.4328
B1=xe2x88x920.0516
B2=xe2x88x920.1436
B3=+0.0153
According to this mode of the invention, a so-called xe2x80x9cplus lensxe2x80x9d provided with a positive refractive power larger than 0 diopter can exhibit an excellent shape stability in its entirety, like in the above-indicated mode (1), since the shape stability generated in the optical zone can be recognized and effectively compensated by the shape stability generated in the peripheral zone with the recognized shape stability in the optical zone utilized. In addition, the peripheral zone is shaped so as to meet specific conditions selected based on the dioptric power given to the optical zone, thus making it possible to establish the excellent shape stability of the contact lens, while assuring a sufficient degree of freedom in designing the optical characteristics of the optical zone, and an excellent lens wearing comfort.
It should be appreciated that the peripheral zone is shaped with the diameter DFOZ of the front optical zone taken into consideration, like in the above-indicated mode (2), making it possible to suitably arrange the shape stability generated in the peripheral zone depending upon the shape stability generated in the optical zone, permitting the contact lens to exhibit both of the excellent shape stability and lens wearing comfort in its entirety. More specifically described, in the case where the optical zone of the contact lens has a relatively large diameter DFOZ, the thickness of a central portion of the optical zone is inevitably made larger sufficiently, since the positive refractive power given to the optical zone is great. Thus, the contact lens can be designed so as to exhibit its entire shape stability by effectively utilizing the shape stability generated in the optical zone, and so as to establish the excellent lens wearing comfort without needing the excessive increase in the thickness of the peripheral zone, which is likely to be caused. In the case where the optical zone of the contact lens has a relatively small diameter DFOZ, on the other hand, the contact lens can be designed such that a tendency of lacking in the shape stability generated in the optical zone can be compensated by the peripheral zone.
(6) A contact lens according to any one of the above indicated modes (1)-(5), wherein at least one of the front junction and the back junction is formed by a connecting surface joined to the optical zone along junctions lying on tangents common to curves of the optical zone and the connecting surface, and to the peripheral zone along junctions lying on tangents common to curves of the peripheral zone and the connecting surface, as seen in diametrical cross section, the connecting surface being a smoothly continuous surface interposed between the optical zone and the peripheral zone and lying on tangents whose slopes are continuously changed over an entire width thereof. According to this mode of the invention, at least one of the front surface and the back surface of the contact lens is arranged such that the optical zone and the peripheral zone can smoothly join together at their junction with the help of the connecting surface interposed therebetween with a given radial width, although the optical zone and the peripheral zone are provided with different shapes in diametrical cross section so as to meet their different optical characteristics, respectively. Thus, the presence of the connecting surface makes it possible to smoothly join the optical zone and the peripheral zone together with no adverse influence on the shape or the optical characteristics of the optical zone and the peripheral zone, thereby effectively eliminating a possible problem of deterioration in lens wearing comfort due to an edge or angle formed at the junction between the optical zone and the peripheral zone on the at least one of the front and back surfaces of the contact lens.
The contact lens of the present invention may have the following structure other than the structure defined by the above-indicated mode (6) for a smooth connection between the optical zone and the peripheral zone. In the case where the peripheral zone of the contact lens has a relatively high degree of freedom in its shape design, at least one of the front and back surfaces of the contact lens is arranged such that an inner circumferential edge of the peripheral zone is shaped to have an angle value equal to an angle value of an outer circumferential edge of the optical zone. This arrangement permits at least one of the front and back surfaces of the contact lens that the optical zone and the peripheral zone directly and smoothly join together along junctions lying on tangents common to curves of the optical zone and the peripheral zone. The contact lens constructed as described above can provide a further improved lens wearing comfort as felt by the lens wearer, like in the above-indicated mode (6) of the invention.
(7) A contact lens according to any one of the above-indicated modes (1)-(6), wherein the front peripheral zone has a diametrical cross sectional shape represented by at least one of a polynomial of not less than second order, a conic section and a spline curve. According to this mode of the invention, the front peripheral zone can be designed to be a smooth surface with a high degree of freedom. This makes it possible to easily shape the front peripheral zone of the contact lens, for example, such that the front peripheral zone is joined to the front optical zone along junctions lying on tangents common to curves of the front optical zone and the front peripheral zone, and is smoothly joined to an outermost edge of the contact lens, while permitting the contact lens to have a desired lens thickness as measured at the back junction where the back optical zone and the back peripheral zone join together.
(8) A contact lens according to any one of the above-indicated modes (1)-(7) wherein the back peripheral zone at least partially has an arcuate shape in diametrical cross section. This arrangement permits a relatively easy designing of the back peripheral zone of the contact lens. Preferably, the back peripheral zone is designed to have a radius of curvature larger than that of the back optical zone. In this respect, the back peripheral zone may consist of at least two parts that have arcuate forms in diametrical cross section with different radius of curvatures, and that join together in the radial direction of the contact lens. In this respect, the radius of curvature of the radially outer one of the two parts of the back peripheral zone is preferably made larger than that of the radially inner one of the two parts of the back peripheral zone.
(9) A contact lens according to any one of the above-indicated modes (1)-(8), wherein the contact lens comprises a soft contact lens formed of a soft material. According to this mode of the invention, the principle of the present invention is applied to a soft contact lens, so that the soft contact lens is accurate in its dioptric power, thin enough to assure a high gas permeability, and is able to effectively establish its shape stability that has been widely required. The soft contact lens of this mode of the invention can eliminate the conventionally experienced problem that a soft contact lens, when being placed on a finger of the lens wearer for wearing the contact lens, clings to a surface of the finger of the lens wearer. Therefore, the soft contact lens of this mode of the invention is excellent in its handling and easy to differentiate between the front surface and the back surface of the contact lens.
All of the above-described modes (1)-(8) of the invention may be applicable not only to a variety of soft contact lenses of high, medium and low hydrophilic types but to hydrophobic or hard contact lenses as well. These contact lenses according to any one of the above-indicated modes (1)-(8) of the invention can be provided with a relatively small lens thickness, each being satisfactory in its strength and deformation stability in its entirety, whereby these contact lenses can satisfactory provide required optical characteristics and can improve lens wearing comfort and handling, and their overall strength.
(10) A method of designing a contact lens including: a central optical zone having a front optical zone and a back optical zone; and a peripheral zone surrounding the optical zone and having a front peripheral zone and a back peripheral zone, the method comprising the steps of: positioning a back junction where the back optical zone and back peripheral zone join together is located radially outward of a front junction where the front optical zone and the front peripheral zone join together; and adjusting a ratio TBJ/TFJ of a back junction lens thickness TBJ to a front junction lens thickness TFJ to be held within a tolerable range predetermined depending upon a dioptric power P provided to the optical zone.
This method of designing a contact lens has been accomplished based on the technical concept as described above with respect to a contact lens according to the present invention. Namely, the back junction where the back optical zone and the back peripheral zone join together is located radially outward of the front junction where the front optical zone and the front peripheral zone join together and the lens thickness at the back junction is suitably adjusted, thus making it possible to establish a desirable shape stability of the contact lens with no adverse influence on the optical characteristics of the contact lens. It should be noted that the configuration of the contact lens is determined based on the dioptric power of the optical zone. This makes it possible to compensate the shape stability at the optical zone by enhancing the shape stability at the peripheral zone, when the shape stability of the optical zone is considered to be insufficient. Accordingly, the present method makes it possible to effectively and easily design a desired lens configuration that allows the contact lens to exhibit desired shape stability in its entirety with a relatively small lens thickness, by adjusting a shape stability generated in the peripheral zone depending upon a shape stabilizing effect generated in the optical zone, with required optical characteristics of the optical zone provided highly precisely.
That is, the method according to this mode of the invention makes it possible to easily provide a contact lens that is remarkably improved both in its handling and wearing comfort while maintaining its accurate optical characteristics. This method may preferably be usable for designing a variety of soft contact lenses of high, medium and low hydrous types, and for designing hard contact lenses as well, thereby allowing each obtained contact lens to be improved in its wearing comfort and its overall handling and strength, while being satisfactory in its optical characteristics.
(11) A method of designing a contact lens according the above-indicated mode (10), further comprising the step of designing a form of the optical zone such that a central lens thickness measured along a center axis of the contact lens is held within a range of 0.03-0.50 mm, more preferably 0.05-0.50 mm, and a peripheral lens thickness measured at the front junction is not less than 0.05 mm, more preferably, 0.10 mm. This method makes it possible to more sufficiently achieve both requirements, i.e., the thinned optical zone and the lens shape stability.
(12) A method of designing a contact lens according to the above-indicated mode (10) or (11), wherein when a dioptric power P is held within a range from 0 diopter to xe2x88x926 diopters, the ratio of TBJ/TFJ is adjusted according to a condition expression that a ratio of the back-junction lens thickness TBJ to the front-junction lens thickness TFJ is held within a tolerable range of not less than 1. As discussed above with respect to the above-indicated mode (2), when the contact lens has a dioptric power ranging from 0 diopter to xe2x88x926 diopters, the optical zone is likely to be insufficient in its shape stabilizing effect so as to be suitably designed in its shape and thickness. This insufficient shape stability generated in the optical zone can be compensated with the shape stability generated in the peripheral zone. Thus, the present method easily permits a design of the contact lens that is excellent in handling with the help of the excellent shape stability in its entirety, while highly ensuring desired optical characteristics of the optical zone and a lens wearing comfort with the help of a relatively thin lens thickness.
(13) A method of designing a contact lens according to any one of the above indicted modes (10)-(12), wherein the tolerable range of the ratio TBJ/TFJ of the back-junction lens thickness TBJ to the front-junction lens thickness TFJ comprises options represented by the expressions with respect to the ratio TBJ/TFJ recited in the above indicated modes (1),(3) and (4), selectable depending upon the dioptric power P given to the optical zone and the diameter DFOZ of the optical zone. The present method of this mode of the invention makes it possible to design and provide contact lenses constructed according to the present invention and capable of exhibiting a variety of excellent technical effects or advantages of the invention.
The contact lens designed according to any one of the above-indicated method of the invention, may be manufactured according to any known methods of producing contact lenses, which may be selected with a material and a dioptric power of the lens taken into consideration. For instance, the contact of the present invention may be formed of polymer by cutting and polishing, or alternatively may be manufactured by injecting and polymerizing a monomer composition in a mold having a mold cavity whose form corresponds to a desired form of the contact lens. Also, the contact lens of the invention may be manufactured by forming one of opposite surfaces thereof upon polymerizing a material in a suitable mold cavity and by cutting and polishing the other surface thereof. Further, the contact lens of the invention may be formed by spin casting wherein a monomer composition is injected into a rotatable mold and shaped by utilizing an effect of a centrifugal force.